[Mk2] [Turbo] Booster/Vacuum issue

[Glenn_k]

When I drive my car on full boost and then rapidly hit the brakes, it is as if my booster is not functioning and my brake pedal is really hard. After a few seconds, the pedal softens and my brake pressure comes back.
I've heard of a one way valve in the brake booster vacuum lines, but where is it located?
Could it also be the main vacuum line from the intake manifold to the booster? I have replaced this completely, but might not have used vacuum hose.

[Peter Gidden]

but might not have used vacuum hose.

Big mistake. Why did you replace? Never had to replace one. Ever.

ETA

Just been thinking. Colour?

[Glenn_k]

I didn't replace it, the previous owner of my car just ripped everything out.
Colour? Just black rubber, nothing fancy.
So do you know where this valve should be located? I have the big brakes..

[Peter Gidden]

The check valve is pressed into the front of the booster unit and i've never known one to fail.

Replace the vac hose for a genuine item. Ordinary hose will most likely collapse under vacuum.

[Glenn_k]

Do you suppose i could replace it with a piece of special vacuum hose? I dont have an OEM item within reach..

[Peter Gidden]

You could try. Or i'll send you one for £10 inc postage.